Unionists say they support a decision by the Irish Government not to allow people in Northern Ireland a vote in the upcoming abortion referendum, despite a legal challenge.

On Monday a judicial review was launched in Dublin's High Court over the referendum on the repeal of the eighth amendment of the Republic's Constitution.

The basis of this legal challenge is the failure of the State to allow Irish citizens here to vote in the poll, which will take place in May.

Solicitor Michael Halleron of Madden & Finucane in Belfast, who is representing the applicant in the case, said the referendum was a "matter of national importance and all citizens on the island of Ireland should be entitled to vote".

Irish citizens living overseas who wish to vote also must travel home in order to do so, as overseas postal voting is only available in limited circumstances.

The referendum will see people decide whether to repeal article 40.3.3 of the constitution, known as the eighth amendment, which gives a mother and her unborn foetus equal right to life.

The amendment, in place since 1983, bans abortion even in cases of rape or where a foetus has a fatal abnormality. Terminations are only allowed when the mother's life is at risk.

Taoiseach Leo Varadkar has pledged that, if the referendum result supports constitutional change, the Irish Government will table legislation for unrestricted abortion in the first 12 weeks of pregnancy.

UUP MLA Doug Beattie acknowledged that a constitutional change could lead to women from here travelling over the border for abortions instead of to Britain.

However, he said that deciding who could vote was up to the Irish Government.

"If the criteria (to vote) is you have to be a resident in the Republic of Ireland then that's the decision of the Republic," he said. "This referendum is about another country's laws. It's a brave decision to hold a referendum, but it's another country." Mr Beattie believes abortion should be decriminalised immediately in Northern Ireland.

"I am in favour of giving women more choice, definitely in cases of fatal foetal abnormality and sex crimes," he added.

"I do think there should be a change in abortion laws here.

"But I wouldn't be keen on a referendum here. I think it would be very divisive, and the political system could still block the outcome."

TUV leader Jim Allister said it would be "absolute nonsense to let anyone but a citizen of the Irish Republic vote" in the referendum.

"It's a decision taken by a foreign jurisdiction to decide their future laws," he insisted.

He also said that he would not be in favour of holding an abortion referendum in Northern Ireland, as "those issues are matters for elected representatives here".

In the absence of an Assembly, he didn't believe that Westminster should legislate to change abortion laws here.

"It's technically a devolved matter," he added.

"They have to have a regard for the distinctive setting and views of each part of the United Kingdom.

"During the 25-30 years of direct rule they never thought it appropriate to bring in the 1967 Abortion Act here."

The judicial review has been scheduled for April 8 to allow all respondents, including the Taoiseach, to be put on notice.